Index: configure.ac
==================================================================
--- configure.ac
+++ configure.ac
@@ -550,10 +550,45 @@
 
 	AC_ARG_ENABLE(compiler-tls,
 		AS_HELP_STRING([--disable-compiler-tls],
 			[disable compiler thread local storage]))
 	AS_IF([test x"$enable_compiler_tls" != x"no"], [
+		AC_CHECK_HEADERS(threads.h, [
+			AC_DEFINE(OF_HAVE_THREADS_H, 1,
+				[Whether we have threads.h])
+		])
+
+		AC_MSG_CHECKING(whether _Thread_local works)
+		AC_TRY_LINK([
+			static _Thread_local int x = 0;
+		], [
+			x++;
+		], [
+			AS_IF([test x"$enable_shared" != x"no"], [
+				old_OBJCFLAGS="$OBJCFLAGS"
+				OBJCFLAGS="$OBJCFLAGS -fPIC"
+				AC_TRY_COMPILE([
+					static _Thread_local int x = 0;
+				], [
+					x++;
+				], [
+					AC_MSG_RESULT(yes)
+					AC_DEFINE(OF_HAVE__THREAD_LOCAL, 1,
+						[Whether _Thread_local works])
+				], [
+					AC_MSG_RESULT(no)
+				])
+				OBJCFLAGS="$old_OBJCFLAGS"
+			], [
+				AC_MSG_RESULT(yes)
+				AC_DEFINE(OF_HAVE__THREAD_LOCAL, 1,
+					[Whether _Thread_local works])
+			])
+		], [
+			AC_MSG_RESULT(no)
+		])
+
 		AC_MSG_CHECKING(whether __thread works)
 		AC_TRY_LINK([
 			/* It seems __thread is buggy with GCC 4.1 */
 			#if __GNUC__ == 4 && __GNUC_MINOR__ < 2
 			# error buggy
@@ -570,19 +605,19 @@
 					__thread int x = 0;
 				], [
 					x++;
 				], [
 					AC_MSG_RESULT(yes)
-					AC_DEFINE(OF_HAVE_COMPILER_TLS, 1,
+					AC_DEFINE(OF_HAVE___THREAD, 1,
 						[Whether __thread works])
 				], [
 					AC_MSG_RESULT(no)
 				])
 				OBJCFLAGS="$old_OBJCFLAGS"
 			], [
 				AC_MSG_RESULT(yes)
-				AC_DEFINE(OF_HAVE_COMPILER_TLS, 1,
+				AC_DEFINE(OF_HAVE___THREAD, 1,
 					[Whether __thread works])
 			])
 		], [
 			AC_MSG_RESULT(no)
 		])

Index: src/OFAutoreleasePool.m
==================================================================
--- src/OFAutoreleasePool.m
+++ src/OFAutoreleasePool.m
@@ -29,11 +29,11 @@
 #import "autorelease.h"
 
 #define MAX_CACHE_SIZE 0x20
 
 #if defined(OF_HAVE_COMPILER_TLS)
-static __thread OFAutoreleasePool **cache = NULL;
+static thread_local OFAutoreleasePool **cache = NULL;
 #elif defined(OF_HAVE_THREADS)
 static of_tlskey_t cacheKey;
 #else
 static OFAutoreleasePool **cache = NULL;
 #endif

Index: src/OFObject.h
==================================================================
--- src/OFObject.h
+++ src/OFObject.h
@@ -44,10 +44,22 @@
 #if defined(__GNUC__)
 # define restrict __restrict__
 #elif __STDC_VERSION__ < 199901L
 # define restrict
 #endif
+
+#if defined(OF_HAVE__THREAD_LOCAL)
+# define OF_HAVE_COMPILER_TLS
+# ifdef OF_HAVE_THREADS_H
+#  include <threads.h>
+# else
+#  define thread_local _Thread_local
+# endif
+#elif defined(OF_HAVE___THREAD)
+# define OF_HAVE_COMPILER_TLS
+# define thread_local __thread
+#endif
 
 #ifndef __has_feature
 # define __has_feature(x) 0
 #endif
 

Index: src/autorelease.m
==================================================================
--- src/autorelease.m
+++ src/autorelease.m
@@ -28,13 +28,13 @@
 #import "macros.h"
 
 #import "autorelease.h"
 
 #if defined(OF_HAVE_COMPILER_TLS)
-static __thread id *objects = NULL;
-static __thread id *top = NULL;
-static __thread size_t size = 0;
+static thread_local id *objects = NULL;
+static thread_local id *top = NULL;
+static thread_local size_t size = 0;
 #elif defined(OF_HAVE_THREADS)
 static of_tlskey_t objectsKey, topKey, sizeKey;
 #else
 static id *objects = NULL;
 static id *top = NULL;

Index: src/objfw-defs.h.in
==================================================================
--- src/objfw-defs.h.in
+++ src/objfw-defs.h.in
@@ -6,11 +6,10 @@
 #undef OF_HAVE_BUILTIN_BSWAP16
 #undef OF_HAVE_BUILTIN_BSWAP32
 #undef OF_HAVE_BUILTIN_BSWAP64
 #undef OF_HAVE_CHMOD
 #undef OF_HAVE_CHOWN
-#undef OF_HAVE_COMPILER_TLS
 #undef OF_HAVE_FILES
 #undef OF_HAVE_FORWARDING_TARGET_FOR_SELECTOR
 #undef OF_HAVE_GCC_ATOMIC_OPS
 #undef OF_HAVE_LINK
 #undef OF_HAVE_MAX_ALIGN_T
@@ -26,9 +25,11 @@
 #undef OF_HAVE_SCHED_YIELD
 #undef OF_HAVE_SOCKETS
 #undef OF_HAVE_SYMLINK
 #undef OF_HAVE_SYS_SOCKET_H
 #undef OF_HAVE_THREADS
+#undef OF_HAVE___THREAD
+#undef OF_HAVE__THREAD_LOCAL
 #undef OF_NINTENDO_DS
 #undef OF_OBJFW_RUNTIME
 #undef OF_UNIVERSAL
 #undef SIZE_MAX